Pop/backfire shifting close to 3k or going up hill

[Rustytruck]

I would be checking the vacuum modulator line, hose and making sure tthere are no leaks. 3000 shift points are usually a forced passing gear sjift or governor forced shift. Make sure the pin is in place behind the modulator and no tranny fluid in the vacuum side of the modulator. Make sure pf downshift screw adjustment on the carb.

 

[Abe Jauregui]

I would be checking the vacuum modulator line, hose and making sure tthere are no leaks. 3000 shift points are usually a forced passing gear sjift or governor forced shift. Make sure the pin is in place behind the modulator and no tranny fluid in the vacuum side of the modulator. Make sure pf downshift screw adjustment on the carb.

I have a three speed column shift

 

[DirtDonk]

I don’t remember if this was mentioned, but do you have full dual exhaust by any chance?
If so what size?

Aside from the possible bad muffler mentioned (very common in fact), you might simply be running lean enough to get some deceleration popping.

And the carb might have a clogged circuit on one side making it leaner on that side.

Just throwing stuff out there to see if anything sticks.

 

[Abe Jauregui]

I don’t remember if this was mentioned, but do you have full dual exhaust by any chance?
If so what size?

Aside from the possible bad muffler mentioned (very common in fact), you might simply be running lean enough to get some deceleration popping.

And the carb might have a clogged circuit on one side making it leaner on that side.

Just throwing stuff out there to see if anything sticks.

No, I have headers into one exhaust

 

[Abe Jauregui]

So I just pulled each spark plug wire with the engine running and the rpms drop a little with each cylinder head so the new wires seem good. The exhaust is a Walker. Wasn’t ver expensive. It’s idles and drives like a champ just has that popping sound when giving it high revs or when changing gears. The only thing I haven’t checked are the header manifold gaskets.

 

[Abe Jauregui]

Found it! Connected a leaf blower I borrowed and followed the hiss sound until I could feel it with my fingers and hear it change as I pass over it. Header gasket! Brand new too.


https://drive.google.com/file/d/1S29eEF75DJmu5hnDyVTI2LlnK9hqgWXA/view?usp=drivesdk

 

[DirtDonk]

OK, that should be good. Definitely at least check the bolts for tightness because they can loosen up overtime. Sometimes not very much time!
Headers themselves can slightly lean out your mixture, but not as much as headers and dual exhaust.
Still, depending upon what jets were in your carburetor to begin with, or what might’ve been swapped in overtime and many owners, you still could be dealing with a slightly lean condition.

I know how to check those things, but I don’t know how easy it would be to find someone that can do a tail pipe sniffer or an O2 sensor to see if you are in fact overly lean.

 

[DirtDonk]

Great detective work!
And a common issue for sure. Maybe you’ll get lucky and just be able to tighten up the bolts and reseal it. But if it’s gone long enough the exhaust gases will have etched a channel into the gasket.

 

[Abe Jauregui]

I added a picture. It did carve out a section of the gasket. Regular fel-pro. Should I upgrade the gasket?

 

[DirtDonk]

I have very minimal experience personally with header gaskets. But based on other peoples experience I would definitely upgrade.
There are quite a few people who have had nothing but great luck with the old fiber gaskets, but far and away more people have trouble with them until they upgrade to a copper or aluminum gasket material.
Multi layer steel even maybe?

One of the old tricks was to soak the fiber gaskets in water before installing. That would cause them to swell but I don’t know how that ended up working because you would think they would eventually shrink.
Seemed to work for some though, but I would still use one of the modern alternatives.
And maybe even locking bolts if you don’t have them on there already.
A few different styles available.

 

[DirtDonk]

I forgot to ask, but we’re any of the header bolts loose?

 

[Abe Jauregui]

I forgot to ask, but we’re any of the header bolts loose?

They actually weren’t. I wonder how the gasket just made blew on one part and created a tunnel

 

[EPB72]

I added a picture. It did carve out a section of the gasket. Regular fel-pro. Should I upgrade the gasket?

As of late I'd suggest REMFLEX as gasket choice they work well ,and also have used on a handfull of customers vehicles that had leak issues that they or someone else hasn't been able to cure..

 

[Abe Jauregui]

As of late I'd suggest REMFLEX as gasket choice they work well ,and also have used on a handfull of customers vehicles that had leak issues that they or someone else hasn't been able to cure..

Installed remflex and the pop is gone! So is the ticking noise. What I noticed is that the first paper gasket has the hooks to hang on the outside bolts where Remflex doesn’t thus giving more seal in the area where it leaked.

 

[EPB72]

Installed remflex and the pop is gone! So is the ticking noise. What I noticed is that the first paper gasket has the hooks to hang on the outside bolts where Remflex doesn’t thus giving more seal in the area where it leaked.

Good deal ..so after a few heat cycles recheck bolts when cold for tightness and after that you should be good to go...but not a bad idea to check from time to time..

 

[Abe Jauregui]

Thank to everyone. What a difference a small thing can be overlooked when building a car as the importance of a gasket and not just getting what was in stock.

 

[DirtDonk]

Congrats on a good find an even better fix.

 

[DC_Gearhead]

Found it! Connected a leaf blower I borrowed and followed the hiss sound until I could feel it with my fingers and hear it change as I pass over it. Header gasket! Brand new too.


https://drive.google.com/file/d/1S29eEF75DJmu5hnDyVTI2LlnK9hqgWXA/view?usp=drivesdk

Awesome idea on the leaf blower! That’s some true Bronco owner creativity.


Sent from my iPad using Tapatalk

 

[Speedrdr]

Okay, I’ve just got to ask about the leaf blower. Where do you hook it up to?? Inquiring minds and all of that.

Randy

 

[gr8scott]

you might simply be running lean enough to get some deceleration popping.

I had this happening some time ago, was driving me nuts. I opened both idle mixture screws 1/16th turn and the popping went away.